VIABILITY OF FIXED TYPE POWER CAPACITORS FOR LOSS REDUCTION IN LOW VOLTAGE (400V) DISTRIBUTION NETWORKS OF POWER UTILITIES A dissertation submitted to the Department of Electrical Engineering, University of Moratuwa in partial fulfillment of the requirements for the degree of Master of Science L IBRARY UNIVERSITY OF MORATUWA, SRI LANKA MORATUWA by CHANDANA WARNAKULASURIYA Supervised by: Dr. JP Karunadasa Department of Electrical Engineering University of Moratuwa, Sri Lanka February 2009 University of Moratuwa 92426 92426 i i i DECLARATION The work submitted in this dissertation is the result of my own investigation, except where otherwise stated. It has not already been accepted for any degree, and is also not being concurrently submitted for any other degree. Name of Candidate: Chandana Warnakulasuriya Date: 05-02-2009 I endorse the declaration by the candidate. . . SrglZr ' / b f r f W ' Name of Supervisor: Dr. JP Karunadasa TABLE OF CONTENTS DECLARATION i TABLE OF CONTENTS "" ABSTRACT iv ACKNOWLEDGMENTS v LIST OF FIGURES vi LIST OF TABLES viii 1 RESEARCH STUDY 1 1.1 Introduction 1 1.2 Objectives 3 1.3 Subject of the eresearch 4 1.4 Area of research 6 2 METHODOLOGY 8 2.1 Base load Reactive power requirement 8 2.2 Selection of the preferred location 8 2.3 Selection of size of capacitor 12 2.4 Selection of voltage rating of capacitors 13 2.5 Selection of ambient temperature category 13 2.6 Reduction of operating temperature of capacitors 13 2.7 Influence of harmonics 16 2.8 Overvoltage due to fixed capacitors 17 3 DATA COLLECTION AND ANALYSIS OF RESULTS 18 3.1 Power flow through Primary substations 18 3.2 Comparison of costs and benefits 19 ii 3.3 Selection of size of fixed capacitor 27 3.4 Selection of voltage rating of capacitors 30 3.5 Assesment of ambient temperature APPLICABLE TO capacitors 31 3.6 Reduction of operating temperature of capacitors 34 3.7 Influence from system harmonics 39 3.8 Overvoltage due to fixed capacitors under low load conditions 45 4 CONCLUSION AND RECOMMENDATIONS 46 Referneces 48 Appendix A 49 Appendix B 50 ABSTRACT The viability of fixed type power capacitors for loss reduction in low voltage (400V) distribution networks of power utilities was studied. Usually, reactive power of the load is compensated at high voltage levels by utility operators, which requires high investment on equipment. This study reveals an alternative low cost reactive power compensation method, which will reduce the capacity requirements of HV reactive power installations. Fixed type power capacitors had been used at the secondary of few of earlier 11 kV/415V distribution transformers in Colombo City distribution system. Most of these units are in operation, even after 20 years of service. But the practice of having fixed capacitors at distribution transformers was not continued thereafter. It was identified through model simulation and field measurements that installation of fixed value power capacitors at feeder pillars of the power distribution network is more economical compared to the earlier practice in Colombo City. The expected minimum energy saving is approximately 300 kWh/month with a 40kvar, 440V rated capacitor installed at the feeder pillar. The main advantages of the proposal are low capital requirement and shorter payback period. The expected maximum payback period is 7 months. In the proposed method, the temperature of operation of capacitors was more critical. The reliability of capacitors is to ensure by adapting measures to reduce the operating temperature of capacitor units, housed in steel enclosures. Encloses, housing capacitor units reduces the case temperature of capacitors. This arrangement was superior to the use of outdoor type capacitors without enclosures. Use of light coloured enclosure with holes for ventilation and thermal insulation will reduce the temperature of operation of capacitor unit at least by 10 °C, compared to dark green finished enclosure with louvers for ventilation and without thermal insulation on the internal surface. Field measurements confirmed that the lifetime of capacitors are not affected due to load harmonics. The maximum harmonic current absorbed by capacitors was 50% lower than the continuous over current rating of the capacitor unit. The simulation of the model with different fixed capacitor sizes shows that there is no risk that transformers would fall into resonance along with fixed capacitors under the load harmonics due to the selected size of capacitors and level of load harmonics. The voltage rise due to fixed type capacitors at no load condition is insignificant for the sizes of capacitors proposed in this study, Hence there is no risk that the power transformers would not fall into ferroresonance due to fixed capacitors. Practical difficulties of usage of LV fixed type capacitors were identified and solutions were recommended so that a cluster of fixed value shunt capacitors can be installed and operated effectively at low voltage distribution level for achieving greater economical benefits. iv 'o. ACKNOWLEDGMENTS I sincerely thank Dr. JP Karunadasa, Supervisor of this research study for his invaluable suggestions and guidance. I specially thank Professor JR Lucus, Dr. NK Wickramarachchi, Dr. SP Kumarawadu and Mr. WDAS Wijayapala for their constructive comments on this study . I also thank Dr. Udawatta for directing us in the proper path so that we could complete our research studies in time. I greatly appreciate Mr. FK Mohideen, AGM (R2), Ceylon Electricity Board who guided me to study the application of fixed type power capacitors for loss reduction in Colombo city. I also thank staff of various branches of Colombo City of Ceylon Electricity Board who helped me to implement the proposed system as a study sample. I also thank the Management of Ceylon Electricity Board for offering me the valuable opportunity of studying for my Masters Degree. LIST OF FIGURES • Figure 1: General arrangement of Colombo City underground distribution system.... 4 Figure 2 : Comparison of distribution losses 6 Figure 3 : Proposed locations for low voltage capacitors 7 Figure 4 : Connection options of low voltage shunt capacitors 9 Figure 5 : Fixed type capacitors in a room of a distribution transformer 9 Figure 6 : Fixed type capacitors at a feeder pillar 9 Figure 7 : Part of network considered for simulation 10 Figure 8 : Total system to represent one transformer supplying two feeders 10 Figure 9 : Sub system to represent one feeder pillar 11 Figure 10 : Sub system for Measuring P, Q, V & I 11 Figure 11 : Effect of enclosure 14 Figure 12 : Use of thermal insulation with reflective foil 15 Figure 13 : Ventilation arrangements with louvers and holes 15 Figure 14 : Power quality analyzer with flexible current transformer 16 Figure 15: Comparison of benefits 23 Figure 16 : Pattern of power flow through a feeder pillar 24 Figure 17 : Verification of energy saving in a feeder cable 24 Figure 18 : Power loss across a feeder cable with capacitor at the end 25 Figure 19 : Power loss across a feeder cable without capacitors 25 Figure 20 : Power loss across a feeder, with and without capacitor 26 Figure 21 : Load curve at the feeder, assumed for simulation 27 Figure 22 : Simulation results for fixed value capacitor at the feeder pillar 28 Figure 23 : Simulation results for fixed value capacitor at the transformer 29 Figure 24 : Power saving under different capacitor values 29 Figure 25 : Variation of lifetime under different voltage ratings of capacitors 30 Figure 26: Thermometers used for field measurement 31 Figure 27 : Distribution of internal air temperature of steel enclosures 31 Figure 28 : Distribution of external air temperature of steel enclosures 32 Figure 29 : Internal to external temperature difference 33 Figure 30 : Indoor and outdoor type capacitors 34 Figure 31 : Temperature logging with and without enclosure 34 Figure 32 : Effect of enclosure 35 vi Figure 33 : Temperature logging to evaluate the effect of exterior colour 35 Figure 34 : Effect of colour on internal temperature 36 Figure 35: Use of thermal insulation and temperature measuring set up :...36 Figure 36 : Effect of thermal insulation 37 Figure 37 : Comparing ventilation arrangements 37 Figure 38 : Holes against louvers for ventilation 38 Figure 39 : Current harmonics absorbed by capacitors 39 Figure 40 : Current harmonics at a feeder pillar 40 Figure 41 : Load harmonics 40 Figure 42 : Level of current harmonics absorbed by capacitors 42 Figure 43 : Model for analyzing the frequency response 43 Figure 44 : Frequency response at a feeder pillar 44 Figure 45 : Frequency response for various capacitor values at the feeder pillar 44 Figure 46 : Frequency response for various capacitor values at the transformer 45 vii LIST OF TABLES Table 1: Statistics of 11 kV & low voltage network 5 Table 2: Daily active power flow from Primary substations in Colombo City 18 Table 3 : Base reactive power flow from Primary substations in Colombo City 19 Table 4 : Comparison of energy saving 23 Table 5 : Upper limit of ambient temperature categories 32 Table 6 : Comparison of harmonic current and THD values 41 Table 7 : Voltage rise under no load condition 45 viii